In a presentation "Advances in molecular sieve technology for natural gas sweetening" by Turnock and Gustafson, presented at the 22nd Annual Gas Conditioning Conference, the University of Oklahoma, April, 1972, conversion of H.sub.2 S into COS has been disclosed, however, such a conversion is considered to be disadvantageous, and concentrating H.sub.2 S in the heavier hydrocarbon fraction has not been disclosed.